Camptothecin (hereinafter, referred to as CPT) isolated from the bark, root, fruit, leaf and the like of Camptotheca acuminata, which is native to China, is a pentacyclic alkaloid, and is known to exhibit antitumor activity by inhibiting nucleic acid synthesis. On the other hand, it has been reported that camptothecin derivatives induce side effects such as diarrhea (‘Gan to Kagakuryoho’ (Cancer & Chemotherapy) 17, p 115-120, 1990) and disorders of the digestive organs; because of these situations, various types of derivatives have been studied with the object of reducing the toxicity, increasing the effect, etc.
The present inventors have already reported, as a compound having suppressed toxicity compared with CPT, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin hydrochloride trihydrate (hereinafter, referred to as CPT-11), which is a water-soluble semisynthetic derivative of CPT and is currently widely used as an antitumor agent (generic name; irinotecan hydrochloride).
Camptothecins such as CPT-11 may be obtained by chemical modification of CPT obtained from natural materials.
However, since the amount of CPT obtained from a natural material such as Camptotheca acuminata, which is a raw material, is extremely small, it is anticipated that it will become difficult to supply a sufficient amount of CPT because of a highly increased demand of CPT-11. Furthermore, preparation methods by total synthesis have been studied, but it is not practical at present.
The present inventors have synthesized 4-iodo-2-methoxy-6-trimethylsilylpyridine-3-carbaldehyde (hereinafter, referred to as compound (b)), which is an intermediate in the synthesis of a tricyclic ketone moiety corresponding to the CDE ring moiety of CPTs, by the scheme below (Patent Publication 1),

however, there is a possibility that it might become difficult to obtain 2-(dimethylamino)ethyl chloride, which is a starting material in the preparation of N-methyl-N-[2-(dimethylamino)ethyl]formamide (FLM) used in this method in the future as it can serve as a starting material in the preparation of a chemical weapon.
On the other hand, alkoxyalkylformamide (formula I) analogs used as formylation reagents of the present invention have been reported (Patent Publications 2 and 3), but these have only been used as starting materials for 6-aminopenicillanic acid or disclosed as a by-product in electrosynthesizing a butanetetracarboxylic acid derivative, and there has been no description at all of their use as formylation reagents.    [Patent Publication 1] WO 02/066416    [Patent Publication 2] JP, B, 51-8955    [Patent Publication 3] JP, A, 2004-514786